This disclosure relates generally to inertial sensing systems, and, more specifically, to inertial sensing systems that include vibratory gyroscopes co-fabricated with an accelerometer and methods of manufacturing the same.
Many known microelectromechanical systems (MEMS) provide a way to make very small mechanical structures and integrate these structures with electrical devices on a substrate using conventional batch semiconductor processing techniques. One common application of MEMS is the design and manufacture of sensor devices. Known MEMS sensor devices are widely used in applications such as automotive, inertial guidance systems, household appliances, game devices, protection systems for a variety of devices, and many other industrial, scientific, and engineering systems. One example of a MEMS sensor is a Coriolis vibratory gyroscope (CVG), which is an inertial sensor that senses angular speed or velocity around one or more axes. Another example is a MEMS accelerometer. MEMS gyroscopes and accelerometers may be used together as an inertial navigation system or inertial navigation unit, in which case accelerometers can be used to calibrate gyroscope drift.
CVGs are subdivided into Class I and Class II gyroscopes. Examples of Class I CVGs are the tuning fork gyroscope and the quadruple mass gyroscope (QMG). At least some known Class I gyroscopes include a relatively large rigid proof mass, which is beneficial for sensing, but also are susceptible to vibrations and shocks that may reduce sensing accuracy. An example of a Class II CVG is a ring gyroscope or a disc resonant gyroscope having a flexible proof mass. Class II CVGs are geometrically symmetrical about their input axis and have identical or nearly identical resonant frequencies for vibration in the drive mode and sense mode directions.
At least some known ring gyroscopes are resistant to vibrations and shocks, but may include a relatively small proof mass consisting of only a single ring, which may cause a high level of mechanical noise and reduce sensing accuracy. As used herein, the proof mass, or drive mass, is the effective mass whose inertia transforms an input angular speed along, or about, an input axis into a Coriolis force. At least some known disc resonant gyroscopes are also resistant to vibrations and shocks. However, despite generally having a larger proof mass than ring gyroscopes, only a small portion of the total proof mass oscillates when the proof mass is excited. Consequently, disc resonant gyroscopes may also suffer from a relatively high level of white noise.